Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art, may produce a flow of exhaust composed of gaseous and solid compounds, including particulate matter, nitrogen oxides (NOx), and sulfur compounds. Due to heightened environmental concerns, exhaust emission standards have become increasingly stringent. The amount of one or more constituents of the flow of exhaust emitted from the engine may be regulated depending on the type, size, and/or class of engine.
One method that has been implemented by engine manufacturers to comply with the regulation of NOx exhausted to the environment is a strategy called selective catalytic reduction (SCR). SCR is a process by which gaseous or liquid reductant (e.g., a mixture of urea and water) is injected into the flow of exhaust from the engine. The combined flow may form ammonia (NH3), which may then be absorbed onto an SCR catalyst. The ammonia on the catalyst may react with NOx in the flow of exhaust gas to form H2O and N2, thereby reducing the amount of NOx in the flow of exhaust gas.
The ability of the SCR catalyst to reduce NOx depends upon many factors, such as catalyst formulation, the size of the SCR catalyst, exhaust gas temperature, exhaust gas flow rate, exhaust gas composition, and urea dosing rate. With regard to the exhaust gas temperature, NOx reduction from the mixture of urea and water may be delayed until the exhaust gas temperature is sufficiently high to avoid urea crystallization and deposit formation. Thus, during cold start and low load conditions, NOx reduction may be limited.
U.S. Pat. No. 9,353,665, issued to Meyer et al. on May 13, 2016 (“the '665 patent”), describes an engine system having an ammonia generating system for an SCR system. For example, FIG. 2 of the '665 patent discloses an ammonia generation system 216, and a reductant dosing module 112 for supplying reductant to a decomposition chamber 104. The ammonia generating system of Mayer uses sonic cavitation or lasers to decompose reductant to ammonia. Such an ammonia generating system may be complex and fail to fully utilize aspects of the engine system to reduce NOx in the engine exhaust gas.
The engine aftertreatment system of the present disclosure may solve one or more of the problems set forth above and/or other problems in the art. The scope of the current disclosure, however, is defined by the attached claims, and not by the ability to solve any specific problem.